Inertial Navigation Advantages • instantaneous output of position and velocity • completely self contained • all weather global operation • very accurate azimuth and vertical vector measurement • error characteristics are known and can be modeled quite well • works well in hybrid systems
Inertial Navigation Disadvantages • Position/velocity information degrade with time (1-2NM/hour). • Equipment is expensive ($250,000/system) - older systems had relatively high failure rates and were expensive to maintain • newer systems are much more reliable but still expensive to repair • Initial alignment is necessary - not much of a disadvantage for commercial airline operations (12-20 minutes)
Inertial Navigation – Basic Principle • If we can measure the acceleration of a vehicle we can • integrate the acceleration to get velocity • integrate the velocity to get position • Then, assuming that we know the initial position and velocity we can determine the position of the vehicle at any time t.
Inertial Navigation – The Fly in the Ointment • The main problem is that the accelerometer can not tell the difference between vehicle acceleration and gravity • We therefore have to find a way of separating the effect of gravity and the effect of acceleration
Inertial Navigation – The Fly in the Ointment This problem is solved in one of two ways 1. Keep the accelerometers horizontal so that they do not sense the gravity vector This is the STABLE PLATFORM MECHANIZATION 2. Somehow keep track of the angle between the accelrometer axis and the gravity vector and subtract out the gravity component This is the STRAPDOWN MECHANIZATION
Inertial Navigation – STABLE PLATFORM The original inertial navigation systems (INS) were implemented using the STABLE PLATFORM mechanization but all new systems use the STRAPDOWN system We shall consider the stable platform first because it is the easier to understand
Inertial Navigation – STABLE PLATFORM There are three main problems to be solved: 1. The accelerator platform has to be mechanically isolated from the rotation of the aircraft 2. The aircraft travels over a spherical surface and thus the direction of the gravity vector changes with position 3. The earth rotates on its axis and thus the direction of the gravity vector changes with time
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- Summer '18